Received: from maia.hub.org (maia-2.hub.org [200.46.204.251]) by mail.postgresql.org (Postfix) with ESMTP id 352521337B49 for ; Mon, 8 Nov 2010 18:13:09 -0400 (AST) Received: from mail.postgresql.org ([200.46.204.86]) by maia.hub.org (mx1.hub.org [200.46.204.251]) (amavisd-maia, port 10024) with ESMTP id 74685-09 for ; Mon, 8 Nov 2010 22:13:02 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from moutng.kundenserver.de (moutng.kundenserver.de [212.227.17.8]) by mail.postgresql.org (Postfix) with ESMTP id B5D891337B43 for ; Mon, 8 Nov 2010 18:13:01 -0400 (AST) Received: from [192.168.1.6] (static-71-179-240-8.bltmmd.fios.verizon.net [71.179.240.8]) by mrelayeu.kundenserver.de (node=mrbap0) with ESMTP (Nemesis) id 0MBZ3e-1PPzXp0DKQ-00ASbs; Mon, 08 Nov 2010 23:13:00 +0100 Message-ID: <4CD875E9.30207@2ndquadrant.com> Date: Mon, 08 Nov 2010 17:12:57 -0500 From: Greg Smith User-Agent: Thunderbird 2.0.0.24 (X11/20100317) MIME-Version: 1.0 To: Scott Carey CC: Marti Raudsepp , Andres Freund , "pgsql-performance@postgresql.org" Subject: Re: Defaulting wal_sync_method to fdatasync on Linux for 9.1? References: <4CCDCAA3.4050805@2ndquadrant.com> <201011010010.28724.andres@anarazel.de> <4CD472CC.80006@2ndquadrant.com> <4CD47FCD.6010106@2ndquadrant.com> <4CD737C1.9070502@2ndquadrant.com> <9D7DB2F2-683B-480C-B781-8D282A280E35@richrelevance.com> In-Reply-To: <9D7DB2F2-683B-480C-B781-8D282A280E35@richrelevance.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Provags-ID: V02:K0:zeGo9JdaKpK5H22HGJYYHWKM6CFok/Twc/U/qzE82dq kZfZQAI/P5sXKQS4As5b327qv9LgyEGeOuMxjDB2kcT8u4vsnf Y5E4TKlSJ4msIHy1K3xmF0C7BIxoUwneEKsIMK7i2SmWkWJ6pW A9NaujESdXkLtfKqavI996A2b0TkMST2HnuLg+im/nKEa6N43/ lt3/xqQhuRpmie1pns1lir/n5RxTcgYJZbJq8QY4+c= X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=-1.89 tagged_above=-10 required=5 tests=BAYES_00=-1.9, RCVD_IN_DNSWL_NONE=-0.0001, T_FRT_PROFILE1=0.01 X-Spam-Level: X-Archive-Number: 201011/113 X-Sequence-Number: 41137 Scott Carey wrote: > Im my opinion, the burden of proof lies with those contending that the default value should _change_ from fdatasync to O_DSYNC on linux. If the default changes, all power-fail testing and other reliability tests done prior on a hardware configuration may become invalid without users even knowing. > This seems to be ignoring the fact that unless you either added a non-volatile cache or specifically turned off all write caching on your drives, the results of all power-fail testing done on earlier versions of Linux was that it failed. The default configuration of PostgreSQL on Linux has been that any user who has a simple SATA drive gets unsafe writes, unless they go out of their way to prevent them. Whatever newer kernels do by default cannot be worse. The open question is whether it's still broken, in which case we might as well favor the known buggy behavior rather than the new one, or whether everything has improved enough to no longer be unsafe with the new defaults. -- Greg Smith 2ndQuadrant US greg@2ndQuadrant.com Baltimore, MD PostgreSQL Training, Services and Support www.2ndQuadrant.us "PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books